Firefox 17 refuses to launch from link in email or desktop shortcut

If FFox is not already running, neither clicking a link in an email (from Thunderbird), nor dbl-clicking a shortcut on my desktop, will launch Firefox. OTOH if FFox is already running then such gestures will create a new tab in the browser and navigate to the indicated URL.

YES, I have already tried temporarily making IE (32-bit) the default browser and then reverting to FFox. Does not fix the defect. And BTW the checkbox "always check to see if Firefox is default" apparently does nothing, because FFox declines to ask (do you want me to be default?).

YES, I have looked at Default Programs inside Control Panel and all 3 web protocols are already set to point to Firefox.

I would appreciate any solution to this or confirmation that this is indeed a defect.

FFox 17.0.1
Win 7 Home Prem 64-bit

Unfortunately I cannot swear that this is a new defect, but...
If FFox is not already running, neither clicking a link in an email (from Thunderbird), nor dbl-clicking a shortcut on my desktop, will launch Firefox. OTOH if FFox is already running then such gestures will create a new tab in the browser and navigate to the indicated URL.
YES, I have already tried temporarily making IE (32-bit) the default browser and then reverting to FFox. Does not fix the defect. And BTW the checkbox "always check to see if Firefox is default" apparently does nothing, because FFox declines to ask (do you want me to be default?).
YES, I have looked at Default Programs inside Control Panel and all 3 web protocols are already set to point to Firefox.
I would appreciate any solution to this or confirmation that this is indeed a defect.
FFox 17.0.1
Win 7 Home Prem 64-bit

Question owner

Thanks to both posters for replying. However, as I said in OP, I have already set FF as default, and checked protocol associations for http, https, etc. Note that when FF process is running, links do cause URL to be rendered in new FF tab.

Also, when the problem occurs, there is no message / error dialog presented, only a silent failure of FF to launch.

The 2 referenced URLs at kb.mozillazine.org are stuffed with details that in a quick reading, seem not to apply. Perhaps other FF users experience this defect and tolerate it, or my particular environment is (hard to believe) somehow special.

Thanks to both posters for replying. However, as I said in OP, I have already set FF as default, and checked protocol associations for http, https, etc. Note that when FF process is running, links '''do''' cause URL to be rendered in new FF tab.
Also, when the problem occurs, there is no message / error dialog presented, only a silent failure of FF to launch.
The 2 referenced URLs at kb.mozillazine.org are stuffed with details that in a quick reading, seem not to apply. Perhaps other FF users experience this defect and tolerate it, or my particular environment is (hard to believe) somehow special.

Question owner

Well, I'm flummoxed. The defect I reported above, now seems to have disappeared. This, without rebooting the PC and without knowingly changing any settings, options, add-ons, etc.
The downside is, I'm mystified; the UPSIDE is, FFox is working properly again.

Well, I'm flummoxed. The defect I reported above, now seems to have disappeared. This, without rebooting the PC and without knowingly changing any settings, options, add-ons, etc.
The downside is, I'm mystified; the UPSIDE is, FFox is working properly again.